Preparation - Brown the ground beef and onion in skillet. Add the minced garlic, tomato sauce, tomato paste, salt and oregano. Mix well and simmer for 2 to 3 minutes. Spray the inside of a crock-pot with non-stick cooking spray. Spoon about one third of the meat sauce in the bottom of the crock-pot. Place about half of the lasagna noodles on top. (break to fit, if necessary). Spoon about half of the remaining meat sauce on top, then half of the Ricotta, half of the Parmesan cheese, and half of the Mozzarella cheese. Repeat layers in the same order, using all of the remaining ingredients. Cover the crock-pot and cook on low for 6 to 8 hours.